The type of muscle tissue that is found in the walls of internal organs like the stomach, small intestine and urinary bladder is called muscle

Smooth muscle, which is involuntary and controlled by the autonomic nervous system (ANS)

Mitochondria produce atp, a high energy compound. atp is used for all sorts of enzyme-mediated reactions, such as making proteins/nucleotides/etc, certain compounds cross the cell membrane, muscles move, etc.  without this source of energy, a cell will die. it will not be able to repair itself, defend against pathogens, etc.